This invention relates to a contact-free optical linear measurement device. More particularly, this invention relates to a measurement device in which a beam path, formed by a beam of light which is emitted by a point source of light and which is displaced parallel in relation to itself, is guided from one side of an object to be measured at right angles in relation to the object to a light sensor through a collective lens on the other side of the object to be measured, with said linear measurement device further having an electronic evaluating unit for determining the length of the object to be measured in the beam path on the basis of the dark and light signals of the light sensor.
Linear measurement devices of this type are for example used for determining the exact diameter of workpieces and are commonly known. As an example of the state of the art the laser-micrometer of Messrs. Oriel GmbH, of Darmstadt, West Germany, which is available on the market and known under the designation "zygo" is mentioned.
In the linear measurement device already known, a laser beam is periodically sent through a collimating lens by means of a rotating mirror. The collimating lens deflects the laser beam in a manner that the beam is displaced parallel to itself as a function of the rotation of the rotating mirror. A collective lens concentrates all beams of light that were received by the collimating lens in one point where a light sensor is positioned.
If an opaque object is held in the space between the collimating lens and the collective lens and provided that beams of light can still get from the collimating lens to the collective lens and hence to the light sensor above and below the object to be measured, the dimensions of the object to be measured can be determined in the plane formed by the beam of light being displaced parallel to itself behind the collimating lens by the rotating mirror by evaluating the period of time during which no beam of light reaches the light sensor.
If, for example, the diameter of a shaft is to be determined by means of a linear measurement device of this type, it is essential that the shaft be exactly vertical in relation to the plane formed by the moving beam of light, since otherwise a greater value would be measured. This exact alignment, however, necessitates great effort and takes up additional time.